Technical Field
The present disclosure relates to a semiconductor device, and can be applied to a semiconductor device that obtains, for example, a ground state of an Ising model.
Background Art
Typically, an improvement in performance of computers depends on the development of semiconductor devices. A current mainstream Neumann-type computer sequentially executes programs, and an increase in an execution speed thereof mainly depends on an improvement in a clock frequency of a processor. However, the improvement in the clock frequency has peaked around 2000, and as an alternative countermeasure for improving the performance, a multi-core processor relying on size reduction of semiconductor devices and parallelization of programs for corresponding thereto are currently being used.
However, the size reduction of the semiconductor device is approaching a limit, and the parallelization of programs that are premised on the sequential execution is about to reach a limit as well. In light of this situation, in order to continuously improve the performance of the computer in future, it is necessary to implement a principle of new information processing which is different from the sequential execution of programs.
By the way, an Ising model is a statistical-mechanical model for describing behavior of a magnetic substance and used for study of magnetic substances. The Ising model is defined as interaction between sites (spins having two values of +1 and −1). Obtaining a ground state of the Ising model in which a topology is a non-planar graph is known as an NP-hard problem.
For this reason, if there is a device capable of obtaining the ground state of the Ising model, it is possible to solve various kinds of problems by converting them into a problem for obtaining the ground state of the Ising model. However, since the obtaining of the ground state of the Ising model is the NP-hard problem as described above, solving it through the Neumann-type computer poses a difficulty in terms of a computation time. An algorithm of introducing a heuristic technique and increasing a speed has been proposed, but a calculation using a physical phenomenon more directly rather than the Neumann-type computer, that is, a method of obtaining the ground state of the Ising model at a high speed has been proposed. As such a device, there is, for example, a device disclosed in Patent Literature 1.
If it is possible to convert a problem that is desired to be solved into the Ising model, more specifically, to convert a problem into an interaction coefficient between sites, it is possible to solve the problem through the above-described analog computer. In the Neumann-type computer of the related art, the problem is expressed by steps, which are sequential in a time direction, called an algorithm, and thus this results in interference with an increase in a speed. However, when the problem is converted into the Ising model, the problem is expressed as a parameter in a spatial direction which is an interaction coefficient between sites, and thus this is suitable for an increase in a speed.
In this regard, it is necessary to implement hardware capable of converting a problem that is desired to be solved into the Ising model and obtaining the ground state of the Ising model.